Support member of nobility on radio (4)
I believe the answer is:
pier
'support member' is the definition.
(I've seen this before)
'nobility on radio' is the wordplay.
'nobility' becomes 'peer' (peer is a kind of nobility).
'on radio' shows a homophone (sound like).
'peer' is a homophone of 'PIER'.
'of' acts as a link.
(Other definitions for pier that I've seen before include "Platform built out from the shore, supported on piles" , "Platform out to sea" , "Promenade over water" , "Seaside structure" , "Load-bearing pillar" .)